This invention relates generally to semiconductor testing apparatuses of the EOS (Electro-Optic Sampling) type for measuring voltages and/or electric fields by making use of the electro-optic effect, and more particularly to such a semiconductor testing apparatus which is capable of carrying out a measurement in terms of one-dimensional distribution and/or simultaneous measurements at a plurality of positions.
Semiconductor testing apparatuses in the related art include, as an example, one described in an article xe2x80x9cHandy-Type High-Impedance Probe Based on EOSxe2x80x9d by Shinagawa et al., Fifteenth Meeting on Light-Wave Sensing Technology, pages 123 to 129, 1995.
FIG. 9 shows an improved version of the above-mentioned semiconductor testing apparatus which will be described hereunder. A light source 1 is driven by a light-source drive circuit 17 to emit a laser light. The laser light emitted from the light source 1 is converged by a collecting lens 2 and guided to a curved-surface mirror 3. The laser light reflected by the curved-surface mirror 3 irradiates an electro-optic element 4. The laser light is then reflected by a reflector 5 provided on the lower surface of the electro-optic element 4, and is split by a polarizing beam splitter 8 into two after passing through a wavelength plate 7. The split laser lights are converged by micro-lens arrays 9-1 and 9-2 and are then received by line sensors 10-1 and 10-2, respectively. The path of the laser light is diagrammatically shown by numeral 18 in FIG. 9.
The light source 1, the collecting lens 2 and the curved-surface mirror 3 are arranged so that the laser light irradiates the boundary surface between the electro-optic element 4 and the reflector 5 in a substantially linear manner. More specifically, the arrangement of the light source 1, the collecting lens 2 and the curved-surface mirror 3 is such that the cross section of the laser light beam on the boundary surface between the electro-optic element 4 and the reflector 5 (hereinafter referred to as xe2x80x9cmeasurement planexe2x80x9d) is substantially a straight line (hereinafter referred to as a xe2x80x9cmeasurement linexe2x80x9d).
Each of the micro-lens arrays 9-1 and 9-2 is in the form of a compound lens constituted by a plurality of lenses which are arranged linearly so that the linear or oblong laser light beam can pass through the plurality of lenses.
A variation in voltage in a DUT (device under test) 6, which the measured device, as brought about by an input to or an output from the DUT 6, causes a change in the electric field in the electro-optic element 4 adjoining the DUT 6. The polarization of the laser light passing through the electro-optic element 4 changes depending on the electric field therein. Since the laser light is linear or oblong as described above, the change in polarization caused by the electric field may be different at different positions in the linear or oblong cross-section of the laser light.
The wavelength plate 7 is chosen such that the laser light has an angle of polarization such that the polarizing beam splitter 8 splits the laser light into two substantially equal parts. The splitting ratio of the polarizing beam splitter 8 changes in accordance with the amount of polarization of the incident light, as a result of which the laser light whose polarization has been changed in the electro-optic element 4 is subject to a change in amplitude when passing through the polarizing beam splitter 8.
As described above, a position-dependant change in the voltage in the DUT 6 results in a change in amplitude of the laser light which depends on the position in the cross-section of the beam. The laser light with a changed amplitude passes through the micro-lens arrays 9-1 and 9-2 and is received by the line sensors 10-1 and 10-2, each of which then converts the change in amplitude of the laser light into a change in amplitude of an electric signal. Thus, electric signals which are proportional to the voltages or electric fields at the respective positions on the DUT 6 can be obtained from each of the line sensors 10-1 and 10-2.
Since the changes in amplitude of the split outputs from the polarizing beam splitter 8 are opposite in phase, i.e., when one increases the other decreases, the signal component of the DUT 6 can be obtained more reliably by taking the difference between the output electric signals from the line sensors 10-1 and 10-2.
For the above reason, as shown in FIG. 9, the output signals of the line sensors 10-1 and 10-2 are first amplified by amplifier circuits 11-1 and 11-2, respectively, and then the difference between the two signals is taken by a differential circuit 26. The differential signal thus obtained is sampled and held by a sample-and-hold circuit 12. The output of the sample-and-hold circuit 12 is supplied through a selection circuit 13 to an A/D converter 14, which converts the output into a digital signal which is fed to a calculation/display device 15. The selection circuit 13 has the function of selecting one out of a plurality of signals. A plurality of amplifier circuits amplify the respectively outputs of the plurality of line sensors in a parallel fashion. Specifically, when the amplifier circuit 11-1 amplifies the output signal of the line sensor 10-1, the amplifier circuit 11-2 amplifies the output signal of the line sensor 10-2 at the same time.
The plurality of output signals of the amplifier circuit 11-1 is supplied to a selection circuit 27-1 which in turn selects one of the plurality of output signals. Similarly, the plurality of output signals of the amplifier circuit 11-2 is supplied to the selection circuit 27-2 which selects the one of the plurality of output signals which has been obtained from the same measurement point as the output signal selected by the selection circuit 27-1. The outputs from the selection circuits 27-1 and 27-2 are added together at the summing circuit 28 to obtain the laser-light intensity signal. The output of the summing circuit 28 is input to the selection circuit 13. These circuits are provided not for the purpose of measuring the DUT 6 but for the purpose of obtaining the intensity of the laser light only, so that a sample-and-hold operation and other operations are not necessary.
If the light source 1 emits a pulsed light, the measurement signal obtained from a measuring zone on the DUT 6, i.e., the output signals from the line sensors 10-1 and 10-2, should be a repetitive signal which is synchronized with a trigger signal St. A timing generator 16 generates a pulse light-emission timing signal Sp, whose phase is delayed by xcex4t each time the trigger signal St is received, to make the light source 1 to emit a pulsed light or a light pulse.
The measurement signals at respective measuring points on the DUT 6, which are obtained by directing the light pulse through the collecting lens 2, the curved-surface mirror 3 and the electro-optic element 4 towards the reflector 5 provided on the upper surface of the DUT 6 to irradiate it, are sampled and held at the same time by the sample-and-hold circuit 12 in synchronism with a sample-and-hold timing signal Ssh.
N signals output from the sample-and-hold circuit 12 are sequentially selected by the selection circuit 13 in accordance with a selection-circuit timing signal Ssel. The A/D converter 14 sequentially converts the analog signals selected by the selection circuit 13 into digital signals in synchronism with the A/D conversion timing signal Sad. Specifically, the N signals as obtained by a single sample-and-hold operation are sequentially A/D converted. By repeating the above operation, results of all the measurements of voltages or electric fields of the DUT 6 can be obtained.
The calculation/display device 15 converts the digital data obtained at the A/D converter 14 into voltages or electric fields at the respective measuring points on the DUT 6 by multiplying the digital data by the sensitivity of the measuring system and displays the voltages or electric fields.
FIG. 10 shows one example of the measurement results which the calculation/display device 15 displays. The example shown corresponds to the case where a voltage distribution on the measurement line of the DUT 6 is displayed as the measurement result. The measurement position is displayed along the horizontal axis in the display area and the voltage values obtained as the measurement results are shown on the vertical axis, whereby a graph showing the relation between the positions and the voltages, i.e., a voltage distribution representation 41, is displayed. In this manner, the relation between the measurement positions and the measured values can be displayed.
If a voltage pulse or electric field pulse moves within the DUT 6, the direction of travel of the voltage or electric-field pulse can be obtained from the change in time of the waveform measured from the DUT 6 and displayed on the calculation/display device 15. FIG. 11 is an example of such a display wherein a waveform representing a voltage distribution is displayed in the display area with the horizontal axis representing the position and the vertical axis representing the voltage. The direction in which each portion is moving is indicated by the traveling direction indications 44 and 45. In this example, the waveform 42 corresponding to the traveling direction indication 44 is shown by a solid line, while the waveform 43 corresponding to the traveling direction indication 45 is shown with a dotted line.
The above-described apparatus in the related art, however, has the following problems. In the measurement results, the voltage distribution in the two-dimensional measurement plane varies with the lapse of time. In other words, a total of four-dimensional axes, namely, two coordinate axes for displaying positions two-dimensionally, a voltage axis and a time axis, are necessary to display the measurement results. However, according to the measuring apparatus in the related art, only two dimensions can be displayed at the same time, and thus it has been impossible to display the measurement results in a sufficiently easily understandable manner. Since the display is thus not easy to understand, it has also been troublesome to operate the measuring apparatus based on the display. Furthermore, it has been impossible to display the direction of movement of the voltage two-dimensionally. Also, it has been impossible to display an energy distribution on the measurement plane (on the two-dimensional plane) as the objective measurement region.
The present invention is to solve the above problems and has an object to provide a semiconductor testing apparatus which can display measurement results in an easily understandable manner.
A semiconductor testing apparatus according to the present invention comprises a measuring section for measuring a change in time of an electric field distribution, a voltage distribution or a current distribution in a measured device, on a desired plane thereof; a display section for displaying a result of measurement on the desired plane of the change in time of the electric field distribution, the voltage distribution or the current distribution of the measured device; and an input section for entering parameters for the display of the result of measurement on the display section; wherein, when an arbitrary measurement time is entered through the input section as a parameter, the display section displays the result of measurement by means of a three-dimensional graph and a representation in numerals, letters or symbols of the measurement time entered through the input section, the three-dimensional graph showing along its three axes a first coordinate in a first direction on the measurement plane of the measured device, a second coordinate in a second direction which is perpendicular to the first direction on the measurement plane, and a voltage at the measurement time entered through the input section at a position on the measurement plane defined by the first and second coordinates.
The measurement results obtained by the semiconductor testing apparatus at the respective measurement times, i.e., the voltage distribution on the measurement plane of the DUT, can thus be displayed on a three-dimensional graph in an easily understandable manner, so that the user of the semiconductor testing apparatus can recognize the measurement results (the voltage distribution on the measurement plane) quite easily.
For example, the display section can display the X-direction position, the Y-direction position and the voltage at an arbitrary measurement time as three-dimensional graphics. In addition, the measurement time to be displayed on the display section can be freely set through the input section.
A semiconductor testing apparatus according to another aspect of the invention comprises a measuring section for measuring a change in time of an electric field distribution, a voltage distribution or a current distribution in a measured device, on a desired plane thereof; a display section for displaying a result of measurement on the desired plane of the change in time of the electric field distribution, the voltage distribution or the current distribution of the measured device; and an input section for entering parameters for the display of the result of measurement on the display section; wherein, when a first coordinate in a first direction on the measurement plane of the measured device or a second coordinate in a second direction which is perpendicular to the first direction on the measurement plane is entered through the input section as a parameter, the display section displays the result of measurement by means of a three-dimensional graph and a representation in numerals, letters or symbols of the first coordinate or the second coordinate entered through the input section, the three-dimensional graph showing along its three axes whichever of the first and second coordinates has not been entered through the input section, a measurement time, and a voltage at a position on the measurement plane defined by the first and second coordinates.
The measurement results obtained by this semiconductor testing apparatus, i.e., the change in time of the voltage (a voltage waveform) on the measurement plane (on a predetermined measurement line) of the DUT, can thus be displayed on the three-dimensional graph in a more easily understandable manner, so that the user of the semiconductor testing apparatus can recognize the measurement results (the change with the lapse of time) quite easily.
For example, the display section can display the Y-direction position, the measurement time and the voltage at an arbitrary X-direction position on the measurement plane as a three-dimensional graphics while the X-direction position can freely be set through the input section. Also, the display section can display the X-direction position, the measurement time and the voltage at an arbitrary Y-direction position on the measurement plane as a three-dimensional graphics, while the Y-direction position can freely be set through the input section.
In the present invention, the display section may be arranged to display two kinds of cursor lines which extend along an X axis representing the X-direction position and a Y axis representing the Y-direction position, respectively, and move over the waveforms displayed as three-dimensional graphics, wherein each cursor line may be movable to an arbitrary position by an input through the input section. A freely movable cursor can thus be displayed on the three-dimensional graph and the measurement values at the cursor position can easily be read out, so that the user can read out any desired measurement value quite easily.
The display section may display the data designated by the cursor line in the form of a two-dimensional graphic representing the position and the voltage. Thus, the parameters at the position of the cursor can easily be read out, so that the user can recognize the parameters at the cursor position easily. For example, the parameters at an arbitrary point on the three-dimensional graph can be displayed, the user can easily see the parameters at an arbitrary point on the three-dimensional graph.
In the present invention, the display section may be arranged to display a point cursor which moves over the waveforms displayed as three-dimensional graphics, wherein the point cursor may be movable to an arbitrary point by an input through the input section. Also, the display section may be arranged to perform a two-dimensional graphics display of the voltage at the point designated by the point cursor and the time.
In the present invention, the power distribution on the measurement plane of the DUT and the distribution of power peaks may be displayed. According to such an arrangement, the user can obtain a variety of information about the DUT.
In the present invention, the display section may be arranged to display markers for designating two arbitrary points on the measurement plane (a two-dimensional plane) so that the direction of movement of the voltage waveform between the two points can be obtained. In order to determine the direction of movement, a Fourier transform is carried out at each of the two points. A matrix of real-term coefficients and imaginary-term coefficients of the first-order frequency components at the two points is obtained, and it is then determined for the adjoining two points at each position that the voltage waveform moves from a greater real-term coefficient side to a smaller real-term coefficient side when the imaginary-term coefficients are positive for the two points, from the smaller real-term coefficient side to the greater real-term coefficient side when the imaginary-term coefficients are negative for the two points, and from a positive imaginary-term coefficient side to a negative imaginary-term coefficient side when the imaginary-term coefficients are positive and negative.
The above determination may be performed for each point on the measurement plane (two-dimensional plane) to obtain a distribution of directions of movement of the voltage waveforms on the two-dimensional plane. In this case, the display section may be arranged to display, by means of vectors, the directions of movement of the voltage waveforms and the power distribution on the two-dimensional plane. More specifically, the vectors can be displayed two-dimensionally with arrows, wherein the magnitude of each vector can be expressed based on the length, the thickness, the color or the like of the arrow. In addition, a threshold may be provided for the power distribution so that the arrows are displayed only at each of those locations where the corresponding power is greater than this threshold.
In this manner, the directions of movement of the voltage waveforms (the directions of movement of the signals) and the amounts of movement of the voltage waveforms can be displayed on a two-dimensional graph representing the measurement plane, so that the user can recognize the directions and the amounts of movement of the voltage waveforms quite easily.